Method and apparatus for universal program controlled bus architecture

ABSTRACT

A programmable logic device is described having an internal three-statable bus and a plurality of driving elements coupled to the internal three-statable bus. Each of the driving elements is operable to drive the internal three-statable bus. The programmable logic device also includes a plurality of interface logic circuits with each of the plurality of interface logic circuits coupled to a different one of the plurality of driving elements. Each interface logic circuit is operable to determine whether the internal three-statable bus is being driven and the interface logic circuits are collectively operable to prevent contention of signals on the internal three-statable bus.

REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/412,975 filed Apr. 11, 2003 now U.S. Pat. 6,781,410, which is acontinuation of U.S. application Ser. No. 10/231,320 filed Aug. 28,2002, U.S. Pat. No. 6,624,658, which is a continuation of U.S.application Ser. No. 09/960,916 filed Sep. 24, 2001, U.S. Pat. No.6,504,399, which is a continuation of U.S. application Ser. No.09/243,998 filed Feb. 4, 1999, U.S. Pat. No. 6,329,839, which is acontinuation of U.S. application Ser. No. 08/708,403 filed Sep. 4, 1996,U.S. Pat. No. 6,034,547.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a programmable, configurable bussystem of liens to interconnect electrical components for anelectrical/electronics system.

2. Art Background

Megacells are described as block components such as static random accessmemory (SRAM), microcontrollers, microprocessors and buffers. Sometimesit is desirable to interconnect a plurality of megacells together toprovide a larger functional entity. One way to interconnect multiplemegacells and logic circuits is through a hardwired bus system. Examplesare illustrated in FIGS. 1 a, 1 b and 1 c. FIG. 1 a illustrates a businterface to a dual port SRAM megacell. Bus lines include DATA0–DATA15,READA0–READA9, WRITEA0–WRITEA9. To couple multiple megacells, the datalines are shared among the coupled cells. However, separate read andwrite lines would be required for each megacell. To the contrary, if themegacells were coupled to generate a deeper combined megacell, the datalines would be separate for each megacell and the read and write lineswould be shared among the megacells. Control signals are then be used toselect a particular megacell for a particular operation. This isillustrated in FIGS. 1 b and 1 c.

Such configurations are hardwired and cannot easily be changed toaccommodate different configurations. Furthermore, if errors occur inthe mask generated, repairs are not easily made, as configurability isminimal. In addition to providing a bus system to interconnect multiplemegacells, tristatable input ports are sometimes used to enable multipleinputs to be input to a particular bus line thus allowing a system levelcommunication between logic to megacells or megacells to megacells.However, a single tristate can directly couple to only one line.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention will beapparent to one skilled in the art from the following detaileddescription in which:

FIGS. 1 a, 1 b and 1 c illustrate interconnections of prior artmegacells.

FIG. 2A and 2B illustrate one embodiment in which logic is programmablycoupled to the megacell.

FIG. 3 is a block diagram illustration of exemplary programmable logicutilized to implement one embodiment of the configurable bus system ofthe present invention.

FIGS. 4A and 4B illustrate the organization of the programmable logic ofFIG. 3.

FIGS. 5A and 5B provide further illustration of the organization of theprogrammable logic of FIG. 3.

FIG. 6 illustrates the programmability of connections to bussed signallines to multiple megacells in accordance with the teachings of thepresent invention.

FIG. 7 a is a block diagram illustration of one embodiment of a megacellconnected to the bus system and I/O.

FIG. 7 b illustrates one embodiment of a dual-port static random accessmemory (SRAM) megacell with a field programmable gate array (FPGA).

FIG. 8 a is a block diagram illustration of an alternate embodiment andFIG. 8 b illustrates the embodiment incorporated into a dual port SRAMwith a FPGA.

DETAILED DESCRIPTION

The system of the present invention provides a flexible programmable busstructure system of lines to couple one or more circuits for input andoutput as well as to each other. In the following description, forpurposes of explanation, numerous details are set forth in order toprovide a thorough understanding of the present invention. However, itwill be apparent to one skilled in the art that these specific detailsare not required in order to practice the present invention. In otherinstances, well known electrical structures and circuits are shown inblock diagram form in order not to obscure the present inventionunnecessarily.

One embodiment of the programmable bus system is illustrated in FIG. 2Aand 2B. The system is illustrated using a megacell circuit; however, itis readily apparent that the system can be utilized with a variety oftypes of circuits and/or components. The type of megacell component usedin the following discussion is a 256×8 dual port static random accessmemory (SRAM). However, the bus system described herein is not limitedto SRAM components. A variety of components, such as microcontrollers,buffers, digital signal processors (DSPs) can be coupled to the bussystem described herein.

FIG. 2A and 2B illustrate one embodiment of the configurable bus systemof the present invention. Referring to FIG. 2A and 2B, the configurablebus system of lines includes groups of lines 210, lines 215, and lines220, 225. Each data input/output port of the megacell 205 is connectedto one line of lines 210. For example, DI[0] is connected to Data[0],DI[1] is connected to Data[1], etc. In addition, each read or writeaddress port of the megacell 205 is connected to one of the group oflines 215. Furthermore, lines 225 are connected to the control ports ofthe megacell 205. It is recognized that the exemplary system describedherein has been programmed to convey address, data and controlinformation across certain of the lines which form the bus system oflines. It is readily apparent that in other applications the system mayonly convey other combinations of information such as data and control.In addition, one skilled in the art recognizes that the lines areprogrammable and can be configured for a variety of types of informationin addition to the types of information described herein.

In the present embodiment, data is preferably input to the megacell 205and output from the megacell through interface logic 230. As will bedescribed below, the interface logic is embodied in a programmable logicdevice, such as a field programmable gate array (FPGA); however, othertypes of logic can be used. A first set of programmable connectionsprogrammably couple the interface logic 230 to the data input/outputports of the megacell 205 (e.g., elements 235, 240, 245, 250). Forexample, programmable elements 235, 240 selectively connect a first line255 from the interface logic 230 to lines Data[0] 211 and Data[8] 212.In addition, in the present embodiment, the programmable elements of thefirst set of programmable elements programmably couple the interfacelogic 230 to line 215. For example, programmable elements 237, 247selectively connect a first line 256 from the input/output logic 230 tobussed lines READA[0] 216 and WRITEA[0] 217. Furthermore, the locationof the programmable elements and the lines that each programmableelement selectively connect to can be varied according to application.FIG. 2A and 2B illustrate one arrangement of programmable elements ofthe first set of programmable elements that provides flexibility inconfiguring the bus system of lines.

The control signals to the megacell 205 can be similarly transmittedover the configurable bus system described herein. A second set ofprogrammable connections are used to selectively connect control signalsreceived from the interface logic 230 to the lines 225 and megacell 205.For example, programmable elements 261, 262 selectively connect a globalclock input to lines 226, 227. In addition, in the present embodiment,lines READA[8], READA[9], WRITEA[8], WRITEA[9] (220 collectively) areused to provide the higher order address bits as control inputs toselect other coupled megacells. This illustrates the capability of thisinnovative bus system to provide system level integration.

Preferably, a third set of programmable connections are used toselectively extend the number of megacells coupled to the configurablebus system. The bus system is configurable using elements of the thirdset of programmable connections to selectively connect on or moremegacells to the bus system of lines. The third set of programmableconnections selectively limit the load on the lines for betterperformance by extending the lines (and therefore increasing the load)only when needed. In the present embodiment, for example, programmableelements 270, 271 selectively extend the lines 210 and lines 215.

In addition, it is preferred that the interface logic 230 isprogrammable and provides bidrectional access to the bus. In addition,it is preferably that the interface logic provides three-statablecontrol to the bus. In particular, control bits and associated logic isused to provide bidirectional, three state control and selectiveinput/output of a plurality of external connections to the lines of thebus system. Referring to FIG. 2, the input/output logic 230 includes aplurality of elements, e.g., 231, 232, 233, 234. Each element is coupledto two external connections 280, 281. Each element is further coupled toenable control signals, e0 282, e1 283. The enable control signals e0,e1 and control bits 284, 285 function to provide the three state busfunctionality that selects one of two external connections for input toor output from the bus. Control bit 284 controls the connection as inputto the megacell 205 and control bit 285 controls the connection asoutput from the megacell 205. If the control bit 284 is set to a firststate, e.g., zero, the three-state connection is disabled. If thecontrol bit 284 is set to a second state, e.g., 1, the state of theconnection is controlled by enable control signals e0, e1 Although thepresent embodiment incorporates the bidirectional, three state access tothe bus system of lines, it is contemplated that bidirectional threestate access mechanism is implemented separate from the interface logic.

The programming of the bus system of lines can be achieved a variety ofways. One method is to manually program the different programmableconnections associated with particular lines of the bus system of lines.Other automated methods are also contemplated. Obviously, onceprogrammed, the programmable connections can remain in the programmedstate. Alternately, a dynamic programmable system can be providedwherein control circuitry coupled to the bus system and the programmableconnections can determine, prior to a data transfer, those connectionsto program in order to configure the bus system of lines to transfer thedata. This control circuitry could reside in a circuit coupled to thebus system for the transfer of data or in a circuit external to the bussystem and connected circuits. For example, the bus system may couple aprocessor or arithmetic logic unit and memory. The processor or ALU cancontain the control circuitry to configure the bus for each datatransfer or plurality of transfers.

Furthermore, it is contemplated that the connections to be programmedcan be determined a variety of ways in order to configure the bus systemfor a general transfer or specific transfers of data. For example, thecontrol circuitry could examine the content of the data to betransferred and the control signals issued prior to or contemporaneouswith a request to transfer or a signal indicating data is to betransferred (e.g., read or write signals or commands) to determine theprogrammable connections to be programmed.

The bus system described can be used to connect components, logiccircuits and the like which span across one or more elements. In thepreset example, as noted above, the bus system is used to connect memory(SRAM) to the logic of a programmable logic device (PLD) such as a fieldprogrammable gate array (FPGA). More particularly, in the presentembodiment, the bus system is used to integrate the memory into the samecomponent as the FPGA. The FPGA, embodied as the interface logic in thepresent embodiment, preferably functions as control logic for accessingthe SRAM or as interface logic between the SRAM and other devices.Preferably, a programmable logic device such as those described in U.S.Pat. No. 5,457,410 and U.S. patent application Ser. No. 08/534,500,filed Sep. 27, 1995 is used.

FIG. 3 is a block diagram of an exemplary FPGA 300. The I/O logic blocks302, 303, 311, and 312 provide an interface between external packagepins of the FPGA 300 and the internal user logic either directly orthrough the I/O to Core interface 304, 305, 313, 314. The externalpackage pins are coupled to the lines of bus system (210, 215, FIG. 2),the signals that are processed through the input/output logic (230 FIG.2), and the ports of the megacell (205, FIG. 2). Four interface blocks304, 305, 313 and 314 provide decoupling between core 306 and logic 302,303, 311 and 312.

The Core 306 includes configurable logic and an interconnect hierarchy.In the present embodiment, the logic is organized in a number ofclusters 307 of logic which are intraconnected by an I-Matrix 301 andinterconnected by MLA routing network 308. The core also includescontrol/programming logic 309 to control the bits for programming theintraconnection and interconnection lines. In the embodiment describedherein, SRAM technology is utilized. However, fuse or antifuse,EEPROM/ferroelectric or similar technology may be used. In order tominimize skewing, a separate clock/reset logic 310 is used to provideclock and reset lines on a group basis.

The present embodiment provides logic in groups called clusters. FIG. 4a is an example of a logic cluster. It is contemplated that the logiccluster illustrated by FIG. 4 a is illustrative and logic cluster can beformed of other elements such as logic gates and flip-flops. Referringto FIG. 4 a, the logic cluster 400 is formed of four logic elements.These elements include one 2 input combinational logic or configurablefunction generator (CFG) 402, two three input CFGs 404, 406 and Dflip-flop 408. CFG 402 can also be a three input CFG. The CFGs 402, 404,406 are programmable combinatorial logic that provide a predeterminedoutput based using two input values (for CFG 402) or three input values(for CFGs 404, 406). The CFGs are programmed with values to provideoutput representative of a desired logic function. The D flip flop 408functions as a temporary storage element such as a register.

This combination of one two input, one output CFG, two three input oneoutput CFGs and a D flip flop enable a variety of logic and arithmeticfunctions to be performed. For example, the elements can be programmedto perform such functions as comparator functions or accumulatorfunctions. In the present embodiment, it is used to selectively couplebus signal lines to input/outputs of a megacell and to input/outputlogic. It should be noted that this combination of elements provides afine granularity without the addition of redundant elements which add tothe die size and speed of processing. Furthermore, the combination ofelements also maximizes usage of elements thereby maximizing usage ofdie size space. The fine granularity characteristic resulting in moreoutput points that can be tapped is a desirable characteristic as oftenan intermediate signal generated by a particular combination of elementsis needed.

In addition, the local interconnect within the cluster is structured toenable signals to be processed with minimum delays. The clusterelements, 402, 404, 406, 408, are connected through interconnectionlines I-M0 through I-M5 (referred to herein collectively as I-Matrixlines) which are oriented horizontally and vertically through the logiccluster. These intraconnections of a cluster are programmable throughswitches, for example switches 420–444. Intraconnections lines I-M0 toI-M5 and switches 420–444 form what is referred to herein as theI-Matrix. The I-Matrix provides connectability among the elements 402,404, 406, 408 to at least one other element of the cluster. For example,the output of the CFG 202 can be connected to the input of CFG 404 byenabling switches 424 and 428.

To ensure minimum signal delays during processing, separate, directconnections are provided between the D flip flop 408 and the three inputCFGs 404, 406. Continuing reference to FIG. 4 a, switches 450–455 andconnected lines provide such connections. It has been determined thatthe input and output of the three input CFGs 404, 406 often performprogrammed functions in conjunction with the register 408. For examplethe three input CFGs can be utilized with the register to provide a onebit multiplexing function.

The bidirectional switches 450–455 can be programmed a variety of waysto route the signal to achieve a specific function. For example, asignal output by CFG 404 can drive D flip-flop 408 by enabling switch451. Alternately, the signal may be driven onto the I-Matrix by enablingswitch 450. Similarly, the output of CFG 406 can drive the input of theD flip-flop 408 by enabling switch 455. Other routing paths byselectively enabling switches are also possible. Furthermore, the outputof the CFG 402 can drive the D flip-flop 408 by an indirect connectionthrough the I-Matrix. Thus, extreme flexibility is achieved.

The routing of the output signal of the D flip-flop is also programmablethrough switches 452 and 453. By selectively enabling switches 452 or453 and selective switches of the I-Matrix, the output signal can berouted to any one of the elements of the cluster or of other clusters.The signal output is selectively routed through the switches 433–435adjacent to the CFG 204 or to switches 441, 442 and 443 adjacent to CFG406. Die savings are achieved without decreasing the level of usage ofelements in the device.

Each logic cluster is connectable to the other logic clusters inside thelogic block through switches extending the I-matrix between neighboringclusters. FIG. 4 b illustrates I-matrix interconnection lines I-M0 toI-M5 of a first logic cluster 460 selectively connected to the I-Matrixlines of adjacent logic clusters 461 and 463, respectively throughswitches 464, 465, 466, 467, 475 and 476.

The flexibility herein described is partially achieved through thenumerous bi-directional switches used. It was also noted previously thatthe switches can be implemented a variety of ways. For example, theswitches can be implemented as fusible links which are programmed byblowing the fuse to open or short the switch. Alternately, the switchcan be a passgate controlled by a bit in an SRAM array. The state of thebits in the array dictate whether a corresponding passgates are open orclosed.

To allow an efficient implementation of a carry chain as well as otherapplications, staggered or barrel connections between clusters is usedto increased connectivity. FIG. 4 b illustrates the extensions of theI-Matrix within a logic cluster to neighboring clusters. For example,switch 475 connects I-M5 of cluster 460 to I-M0 of cluster 461 andswitch 476 connects I-M1 of cluster 460 to I-M2 of duster 461.

A plurality of interconnected logic clusters form a logic block. In thepresent embodiment each logic block consists of four logic clustersorganized in a 2×2 array as generally illustrated by FIG. 5 a. Eachlogic block has a set of bi-directional routing lines to which all CFGsinside the logic clusters are programmably connected. The bi-directionalrouting lines provide the path for signals to travel into and out of thelogic block to the routing lines of a hierarchical routing architecturehaving multiple lengths of interconnections at different levels of thehierarchy. It can also be seen that the block connectors can alsoprovide connections among the CFGs of the logic clusters of the sameblock and adjacent blocks. Although the input and output of each elementof each logic cluster of the logic block can be selectively connected toeach block connector, to control the expansion on die size it ispreferred that each input and output is selectively connected to asubset of block connectors. An example of such an embodiment is shown inFIG. 5 b.

Referring to FIG. 5 b, a symbolic representation of one embodiment ofthe connections to block connectors within a block 300 is shown. Eachelement of each cluster 500, e.g., CFG1, CFG2 and CFG3 is connected totwo identified block connectors (BC) at the inputs. Two block connectorsare identified as coupled to the output of the two input CFG1 and threeblock connectors are coupled to the output of the three input CFGs(CFG2, CFG3). The specific block connectors coupled to each elements aredistributed among the elements of the block to maximize connectivity.

The block connectors provide the input and output mechanism forinterconnecting to higher levels of connections of the routing hierarchyreferred to as the multiple level architecture (MLA) routing network.The network consists of multiple levels of routing lines (e.g., MLA-1,MLA-2, MLA-3, MLA-4, etc.) organized in a hierarchy wherein the higherlevel routing lines are a multiple longer than the lower level routinglines. For example, MLA-2 routing lines are twice as long as MLA-1routing lines and MLA-3 routing lines are twice as long as MLA-2 routinglines and MLA-4 routing lines are twice as long as MLA-3 routing lines.

Using the logic and interconnect hierarchy described, the user canprogram the PLD and the bus to access the memory in a variety ofconfigurations without requiring significant space on the component.

The flexibility and utility of the configurable bus system of thepresent invention is illustrated with reference to FIG. 6. FIG. 6 showsthe bus system configured to couple to 4 SRAM megacells arranged in a2×2 configuration. The programmable elements are configured as passgatescontrolled by a bit in one of the SRAMs or other coupled memory. As isillustrated, no extra logic or interconnect is required for the bussystem configuration. By enablement of the proper links which controlthe interconnect, the bus system is easily configured for the particulararrangement of megacells.

In the present example, the bus system is programmed to be coupled tothe interconnect of the PLD (e.g., block connectors (bc), I-matrix lines(IM) and MLA lines (MLA-1)) to enable the logic of the PLD to providethe necessary interface logic to interface the SRAM to components ordevices external to the system. For example, the PLD provides logic toassert the necessary control signals to transmit the address informationand receive and transmit data. In the example shown in FIG. 6, data andaddress information is communicated through the bi-directional blockconnectors. Control information, including control signals to controlthe state of the enable signals (e0, e1) are communicated via theI-matrix and MLA-1 lines.

FIG. 7 a is a block diagram illustration of one embodiment of megacell701, 702, coupled to the bus system of the present invention. A programcontrolled interface 703, 704, to the bus system of lines 705 andmegacells 701, 702 are provided. The interface from the core bus 705 tothe I/O 706, 707 can be achieved using hardwired or program controlledconnections 708, 709. Preferably, these connections are achieved using aprogrammable, peripheral bus system of lines 710, 711 to provide furtherflexibility. The peripheral bus system is preferably programmable in thesame manner as described above with respect to FIG. 2. In the presentembodiment, the interface logic (230 FIG. 2) provides the programcontrolled interface 703, 704 to the bus system 705 which is alsoprogrammed controlled.

FIG. 7 b depicts an overview of an exemplary component configured withdual port SRAM megacells and a FPGA. The FPGA, including itsinterconnect structure, is represented by elements 712, 715, 720, 725.Each element 712, 715, 720, 725 comprises a plurality of logical blocksorganized in 16×16 array with a corresponding hierarchical interconnectstructure as discussed in U.S. Pat. No. 5,457,410 and U.S. patentapplication Ser. No. 08/534,500. The FPGA elements 712, 715, 720, 725are connected by the interconnect, e.g., block connectors, I-matrixlines and MLA lines (see FIG. 6), through the configurable bus system oflines (e.g., as represented by elements 730, 735, 740) to an SRAM (e.g.,745, 750, 755, 760). SRAM 745, 750, 755, 760 and elements 730, 735 and740 correspond to the structure illustrated by FIG. 6. It should benoted that the bus system preferably spans the entire component to theadjacent array of SRAMs 775, 780, 785, 790 through programmable elements(not shown). The bus system is further coupled to I/O ports or pads(e.g., 791, 792) for input/output to/from the system to externalcomponents or devices. Although the bus system can be coupled throughhardwired connections, it is preferred that the connection be made viaprogrammable elements, e.g., 765, 770 and bus system of lines 775.

FIG. 8 a is a block diagram illustration of an alternate embodiment inwhich gateway interface logic 801 is used to interface the core bussystem 802 to the I/O 803. In addition, this diagram illustratesalternative programmable connections that can be implemented to providefurther programmability and flexibility to the system.

The gateway interface logic 800 is composed of hardwired logic, metalprogrammable logic, or programmable logic such as a plurality of logicclusters and is directly or indirectly coupled (i.e., direct hardwiredconnections or indirect program controlled connections) to the megacell804. FIG. 8 a shows the gateway interface logic 800 is coupled to themegacell 804 via peripheral bus 805 which preferably includesbidirectional, three-statable connections (e.g., 808). The gatewayinterface logic 800 provides an additional level of logic to theinterface between the megacell and the I/O pads or ports to externalcomponents or devices. The gateway interface logic can enable fastertransfer of information. For example, the gateway interface logic can bestructured to provide the specific bus protocols or handshaking requiredto interface to external devices. The gateway interface logic can alsoprovide address decode functionality (e.g., wide decode) to expediteprocessing of information.

In the present embodiment, the gateway interface logic 800 isimplemented as a logic cluster 801, consistent with the logic clustersreferred to herein and in U.S. Pat. No. 5,457,410 and U.S. patentapplication Ser. No. 08/534,500. I-Matrix lines are used to connect thegateway logic to the peripheral bus 805. It should be recognized thatthe gateway interface logic is not limited to the specificimplementation described herein and a variety of logic implementationscan be used.

FIG. 8 b illustrates dual port SRAMs with FPGA and the configurable bussystem. In this embodiment, further programmability is provided at theI/O ports of the system using gateway interface logic. In particular,the programmable gateway logic (e.g., 830) is located between the corebus system of lines (e.g., elements 810, 815, 820) and the I/O (e.g.,825). In the present embodiment a logic duster as illustrated in FIG. 4a is used; however, as noted above, it is contemplated that other formsof logic can be utilized. In addition, this embodiment includes aperipheral bus system of lines 840, which functions is a manner similarto the core bus system of lines providing a programmable bus system fortransferring information. Preferably, each of the programmableconnections of the bus system (e.g., 846, 847) are bidirectional,three-statable connections.

Further enhancements and interconnect flexibility is achieved byproviding programmable connections from the core bus (e.g., 820) directto the peripheral bus 840 and from the megacell (e.g., 845) direct tothe peripheral bus 840. For example, programmable connection 822selectively enables the bus element 820 to be connected to peripheralbus 840. Similarly, programmable element 824 selectively connectsmegacell 845 directly to peripheral bus 840. Such flexibility isadvantageous when speed is a consideration. For example, it may bedesirable to directly connect externally received control input data tothe megacell.

The invention has been described in conjunction with the preferredembodiment. It is evident that numerous alternatives, modifications,variations and uses will be apparent to those skilled in the art inlight of the foregoing description.

1. A programmable logic device, comprising: an internal three-statablebus having conductors; a plurality of interface logic having at leastone logic control signal, each of the plurality of interface logiccomprising at least one driving element, wherein the at least onedriving element is configured to couple to the conductors of theinternal three-statable bus, wherein the at least one driving element isoperable to drive the internal three-statable bus, and wherein the atleast one driving element is coupled to the at least one logic controlsignal of the plurality of interface logic; and support circuitrycoupled to the internal three-statable bus and the at least one drivingelement, wherein the support circuitry comprises: a different set ofdrivers for each driving element, wherein each of the plurality ofinterface logic circuits is coupled to a different one of the set ofdrivers.
 2. A programmable logic circuit, comprising: a plurality oflogic array blocks, wherein each of the plurality of logic array blockscomprises: a plurality of logic cells each having a plurality of inputsand an output, and a plurality of interconnect conductors selectivelycoupled to the plurality of inputs and the output of each of theplurality of logic cells, the plurality of interconnect conductorscomprising: a first type of conductor to couple to more than one logiccell output; and a second type of conductor to couple to a single logiccell output; and a plurality of multiple spans of conductors coupled tothe plurality of logic array blocks and circuit input/output terminals.3. An electronic system, comprising: a processing unit; the programmablelogic circuit of claim 2; a memory unit to store data; an interface; anda bus network to provide communication links between the processingunit, the memory unit and the interface.
 4. The electronic system ofclaim 3, wherein the processing unit is operable to configure theprogrammable logic circuit.